This invention relates to block methods and apparatus for the adaptive quantisation of data and in particular but not exclusively to such methods and apparatus for the block adaptive quantisation of radar data.
In a typical pulse compression radar system, radar data is captured, converted to digital form, compressed and downloaded to a ground station for reconstruction and analysis of the data. The data from a pulse compression radar is characterised by having a gaussian noise-like distribution and so normal compression techniques such as the JPEG format are unsuitable. Accordingly a different form of compression is required and Block Floating Power Quantisation (BFPQ) or Block Adaptive Quantisation (BAQ) is often used. It is used to compress the data generated by the reception chains so that the data rate is low enough to be handled by the subsequent logic circuits.
In a typical synthetic aperture radar using BAQ compression, sample pairs are compressed using a block adaptive quantisation algorithm The BAQ algorithm operates on successive blocks of data, of known length The exponent for each block of data is calculated by summing the total of both the samples of the block and determining an exponent value.
The sample data is divided by the exponent value and this is done by using look-up tables. However, in a typical application for the Advanced Synthetic Aperture Radar (ASAR) developed for the European Space Agency, a BAQ device had a block size of 63 sample pairs, and required a large number of look-up tables (256) to produce the exponent and the compressed digital values. Also the operating speed of the device was slow in view of the large number of look-up tables required.